Pressure indicator

ABSTRACT

An inexpensive and yet highly reliable device for indicating when the pressure in a receptacle is above or below a predetermined value comprises a housing means, a diaphragm means in the housing means, the diaphragm means having first and second side surfaces and a translucent viewing means having an inner surface, at least a portion of which is adjacent to the second surface of the diaphragm means. The first side surface of the diaphragm is adapted to be in pressure communication with the receptacle so the the diaphragm means may be movable between a first position in which the pressure is below a predetermined value and a second position in which the pressure is above a predetermined value. The inner surface of the viewing is relatively frosted except for at least one portion or area which is relatively clear so that when the diaphragm is in the second position it will be in contact with the inner surface of the viewing means and obscure the differences between the relatively frosted portion and the relatively clear portion. With the diaphragm in the second position the second surface of the diaphragm will be clearly visible through the viewing means and hence indicia on the second surface may be easily read. In one embodiment the word &#39;&#39;&#39;&#39;full&#39;&#39;&#39;&#39; may be used. In the first position with the second surface out of contact with the inner surface of the viewing means the relatively clear area will be readily distinguishable from the relatively frosted area. If the relatively clear area forms the word &#39;&#39;&#39;&#39;empty&#39;&#39;&#39;&#39; this may be clearly read.

I United States Patent [151 3,675,722 Balmes, Sr. 1 July 11, 1972 54]PRESSURE INDICATOR [57] ABSTRACT [72] Inventor: Mark E. Balmes, Sr.,Chamblee, Ga. An inexpensive and yet highly reliable device forindicating 'when the pressure in a receptacle is above or below a [73]Asslgnee' Gene! t Extinguisher Corporation predetermined value comprisesa housing means, a diaphragm Northbmo means in the housing means, thediaphragm means having first [22] Filed: April 5, 1971 and second sidesurfaces and a translucent viewing means having an inner surface, atleast a portion of which is adjacent to PP 131,162 the second surface ofthe diaphragm means. The first side surface of the diaphragm is adaptedto be in pressure communi- Related Application Dab cation with thereceptacle so the the diaphragm means may be [63] Continuation of Ser.No. 794,866. Jan. 29, 1969, movable between a first position in whichthe pressure is abandoned. below a predetermined value and a secondposition in which the pressure is above a predetermined value. The innersur- [52] U.S. CI 169/30, 73/406, 1 16/70, face of h i ng is relativelyfrosted except for at l s one 222/23, 239/74 portion or area which isrelatively clear so that when the 51 Int. (:1. ..A62c 11/00, G011 19/12diaphragm is in the eeeend Position it will be in eenteet with 58 Fieldof Search ..169/30, 31 R, 31 1*;239/71, the inner eurfeee of the viewingmeans and obscure the 239/74; 73/388, 1 [6/34, 70 117; 222 23 ferencesbetween the relatively frosted portion and the relatively clear portion.With the diaphragm 1n the second posi- 56] References Cited tion thesecond surface of the diaphragm will be clearly visible through theviewing means and hence indicia on the second UNITED STATES PATENTSsurface may be easily read. In one embodiment the word full" may beused. In the first position with the second surface out ofcontact theinner Surface of the viewing means the 3,088,522 5/1963 Zeuner; "169/31relatively clear area will be readily distinguishable from the 3,134,4455/1964 flofchklss 116/70 x relatively frosted area. If the relativelyclear area forms the 3,241,514 3/1966 Gnm1and.... ..l l6/70 word h may bclearly read. 3,372,501 3/1968 Greene ..116/7O X 15 Claims, 5 DrawingFigures Primary Examiner-M. Henson Wood, Jr. Assistant Examiner-MichaelY. Mar Attorney-Axel A. Hofgren et a1.

2 3 Z0 k 3% 4e 44 59 V 42 37 22 I A Z/ I J "1 i 49 P'ATE'NFEDJUL 1 1I972 INVENTOR. MEK 5. 544.4455, SR.

B%;%, a, Q MWRNEYS PRESSURE INDICATOR CROSS-REFERENCE TO RELATEDAPPLICATION This application is a continuation of application, Ser. No.794,866, filed Jan. 29, 1969 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventiongenerally relates to pressure indicators, and more particularly refersto a device for visibly indicating a pressure in a receptacle meanswhich is above or below a predetermined value.

2. Description of the Prior Art Means for indicating the pressure offluids and materials within a receptacle are, of course, well known inthe prior art. Thus, the prior art includesdevices for indicating aspecific pressure over a given range or for indicating that a pressureis above or below a preselected value. Most of these require specialseals, valving, etc. and are relatively complicated and expensive tomanufacture. Certain applications of pressure indicating devices howevermerely require indication of whether a pressure within a vessel is aboveor below a preselected value. One such application of a pressureindicator may be found in the fire extinguisher art, and particularlywith reference to fire extinguishers utilizing pressurized chemical fireextinguishing materials wherein it is important for safety purposes tohave an indication of whether the material contained within the fireextinguisher is at a sufficient pressure to be effectively discharged inthe time of need. Heretofore, to my knowledge, fire extinguishers of thepressurized chemical type have usually been equipped with a relativelyexpensive and complicated standard bourdon tube-type pressure indicatorhaving a needle which rotates to indicate the condition on a dialdivided into appropriate ranges as, for example, Full and Empty orDischarged, Operable and Overcharged.

There has therefore existed a need for a much less expensive and yethighly reliable pressure indicating means. This need has goneunrecognized and/or unfilled with the result that costs of fireextinguishers have been higher than they have had to be. As a resultperhaps many who would have bought fire extinguishers have not done soand may have suffered an otherwise avoidable detriment due to fire.

SUMMARY OF THE INVENTION A pressure indicator constructed in accordancewith the principles of the present invention generally includes adiaphragm means such as an oil-canning disc. Such diaphragm or disc offlexible material may have a centrally disposed, domed portion movablefrom a first or what may be called its free or normal, convex position,to a second or concave position in response to an increase in pressureabove a preselected value applied to a first side thereof or inwardly ofthe domed portion in the normal convex position, and a translucentviewing means or window member having an inner surface juxtaposedrelative to the diaphragm means and formed with a configurationcomplementary to the domed portion. The dished surface of thetranslucent window is frosted except for at least one portion which isrelatively clean or transparent.

The diaphragm means and the viewing means are retained within anappropriately formed housing which may be sealed into an aperture formedin a side wall of a pressure vessel. Also, the pressure indicatorhousing may include an appropriately formed coupling member engaging afitting formed on the pressure vessel. In either case, a first sidesurface of the diaphragm means disposed oppositely of the translucentwindow is in fluid communication with an interior of the pressurereceptacle in a manner to permit the pressure of the fluid containedwithin the receptacle to act upon the diaphragm means.

When a pressure indicator constructed in accordance with the principlesof the present invention is utilized to indicate an amount of pressurecontained within a fire extinguisher, the

diaphragm means may be designed so that the centrally disposed domedportion moves from the first position to the second position wheneverthe pressure within the fire extinguisher exceeds a pressure whichresults when the extinguisher contains a sufficient amount ofpressurized fire extinguishing material to properly function. Also, thediaphragm means should be designed to return to the normal convexposition in response to a decrease in pressure resulting from the fireextinguishing material being sufficiently discharged to render theextinguisher inoperable. In one embodiment, the diaphragm means movesinto tight engagement with the frosted inner surface of the translucentviewing means whenever the fire extinguisher is under full operatingpressure and hence the indicia "FULL will be readily distinguishable toone viewing the device.

With the diaphragm in tight engagement with the partially frostedsurface of the translucent window, visible distinctions between theclear and frosted areas are obliterated and the window presents auniformly appearing character. Also, with the diaphragm out ofengagement with the partially frosted surface, the surface of thediaphragm becomes visible through the clear areas and the frosted areasappear clear. In this manner, a pressure indicator constructed inaccordance with the principles of the present invention provides meansfor readily ascertaining whether pressure within a vessel is above orbelow a preselected value.

When applied to a fire extinguisher, the clear areas fonned on thepartially frosted surface may be configured to indicate a word, forexample, EMPTY. Furthermore, indented portions formed on the surface ofthe oil-canning disc will be visible through the frosted areas wheneverthe oil-canning disc is in tight engagement with the domed, partiallyfrosted surface of the translucent window, and therefore, theoil-canning disc may include indentations forming a word, for example,FULL, formed either directly on the oil-canning disc or on a flexiblemember adhered to the disc.

Accordingly, it is a primary object of the present invention to providea device for indicating pressure above or below a preselected value andincluding a disc member movable into and out of engagement with apartially frosted surface of a translucent window member in response toan increase or decrease in pressure above or below the preselectedvalue.

BRIEF DESCRIPTION 00 THE DRAWINGS gagement and out of engagement with apartially frosted surface of a translucent window; and

FIG. 5 is an enlarged view of a translucent window utilized in thepresent invention illustrating a partially frosted surface thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, there,is shown a tire extinguisher generally indicated at 10 and including acylinder I 1 containing a pressurized fire extinguishing material and anoutlet control valve 12. The cylinder 11 may be constructed of twohalves telescoped together and sealed by brazing or other suitablesealing means. The outlet valve 12 threadingly engages an appropriatelyformed fitting l3 brazed or otherwise sealed into an aperture formed inan upper domed wall 14 of the cylinder 11. The outlet control valve 12has a manually operable actuating handle 16 by means of which the supplyof fire extinguishing material within the cylinder 11 may be containedtherein, a pressure indicator may be utilized for this purpose.Accordingly, the fire extinguisher may include a pressure indicatorgenerally designated at and sealed within an appropriately formedaperture in a side wall of the cylinder 11.

In accordance with the principles of the present invention, the pressureindicator 20, as illustrated in detail in FIGS. 2 through 5, may includea diaphragm means or disc 21 and a translucent viewing means or window22. The cylinder 11 has a circular aperture 23 formed therein forreceiving the pressure indicator 20. A housing 24 has a cylindricalportion 26 sized to tightly engage the aperture 23 and also has anenlarged cylindrical portion 27 forming an annular shoulder 28 whichengages an outer surface as at29 of the cylinder 11. The housing 24 issealed into the aperture 23 by beads of brazing material as at 31 and32, or other suitable sealing means.

The housing 24 has a centrally disposed throughbore 33 characterized bya reduced portion 34 forming an interior annular shoulder 36. Thediaphragm 21 has an annular peripheral portion as at 37 seated againstthe shoulder 36 and sized to snugly fit within the throughbore 33. Also,the translucent window means 22 includes a cylindrical rim portion 38sized to fit'within the throughbore 33. The rim portion 38 forms aplanar, annular surface 39 seated against the annular portion 37 of thedisc 21 on a side thereof opposite the shoulder 36. Also, the rimportion 38 of the translucent member 22 is characterized by a generallyaxially extending, annular projection 41 engaged by .a retaining ring 42in a manner to squeeze the translucent window 22 and the disc 21 betweenthe retaining ring and the shoulder 36 of the housing 24 for maintainingthe various elements of the pressure indicator 20 in an assembledrelationship.

The retaining ring 42 has a centrally disposed throughbore 43 alignedwith the translucent window 22 to permit substantially the entire windowto be visible therethrough. Also, the retaining ring 42 has externalthreads as ,at 42 formed on an outer periphery thereof engagingcomplementary internal threads as at 46 formed on an outermost endportion of the bore 33 of the housing 24. Although the housing 24 andthe retainingring 42, as illustrated in FIG. 2,. includes threaded means44 and 46 for retaining the ring within the housing, the retaining ringmay be secured within the housing by other suitable means, for example,by staking.

It is contemplated by the present invention that the diaphragm means 21may have a first and second side surface. In one embodiment it is' anoil-canning disc, Le. a disc having a centrally disposed, domed portion47. The diaphragm means 21 is movable from a first or convex positionwhich it will assume with pressure below a predetermined value (asillustrated by dash lines in FIG. 2) to a second, or concave position(as illustrated by solid linesin FIG. 2) in response to a pressure abovea preselected value applied to the first side or inwardly of the domedportion in the normal convex position.

Whenevcr pressure forces on the first side surface or domed portion 47decrease below. the preselected value, which value depends upon theflexibility and thickness of the selected material and the curvature ofthe dome, the domed portion will abruptly move to the first or normalconvex position. This flexing movement is characteristic of the bottomwall portion of an oil dispensing can, and thus, the term oil-canning"disc. When the pressure indicator 20 is utilized to indicate thepressure and the effective amount of pressurized fire extinguishingmaterial contained within a fire extinguisher, such as 10, theoil-canning disc 21 may be configured to move from the normal convexposition, shown by dash lines, to the concave position, when asuflicient amount of pressurized fire extinguishing material iscontained within the cylinder 11 to render the extinguisher 10 operable.Since the pressure within the cylinder 11 changes proportionally to theamount of pressurized fire extinguishing material contained therewithin,the disc 21 in effect moves in response to the pressure within thecylinder 11. Accordingly, the preselected pressure required to move thedomed portion 47 from the normal convex position to the concave positionis determined by the pressure resulting from a minimum amount ofpressurized fire extinguishing material which renders the extinguisher10 operable.

Also, in accordance with the principles of the present invention, thetranslucent window 22 has a surface 48 formed with a dishedconfiguration complementary to the configuration of the domed portion 47of the disc 21 and positioned juxtapositionally to the disc. The domedsurface 48 is partially frosted to provide both frosted areas and clearareas, generally designated at 49 and illustrated as at indentation forclarity. Whenever a surface is tightly engaged with the partiallyfrosted surface 48, visible distinction between the frosted and clearareas is obliterated when the translucent window 22 is viewed from aside opposite the frosted surface.

Accordingly, whenever the amount of pressurized fire extinguishingmaterial contained within the cylinder 1 l generates a pressure greaterthan the preselected pressure causing the dome portion 47 of the disc 21to move into tight engagement with the partially frosted dished surface48, the clear areas 49 become visibly indistinct from the frosted areasand the window 22 presents a uniformly appearing character. 0n the otherhand, whenever the domed portion 47 of the disc 21 is out of engagementwith the partially frosted surface 48 due to the pressure within thecylinder 11 being below the preselected value, the frosted areas appearwhite and the clear areas 49 transmit light reflected from the disc 21,and thus, are distinctly visible.

When the pressure indicator 20 is utilized to indicate the amount ofpressurized fire extinguishing material contained within a fireextinguisher such as 10, the clear areas 49 may be formed in a manner tospell the word EMPTY", as illustrated in FIG. 5, and thereby to providea positive visual indication of a discharged state or inoperability ofthe fire extinguisher 10.

Also, in accordance with the principles of the present invention, anovel means is provided for indicating a charged or operable conditionof the fire extinguisher. This indicating means includes a sheet formedmember 51 adhered to an outermost side surface of the disc 21 to bejuxtapositionally related to the translucent window 22. The sheet formedmember 51 has a size and a configuration to be coextensive with the disc21 and to move with the domed portion 47. An outermost side surface 52of the flexible member 51 contains indentations as at 53 which may formthe word FULL. Desirably, the indentations 53 are differently coloredrelative to the remainder of the surface 52 and horizontally spaced fromthe clear areas 49 of the partially frosted surface 48.

Accordingly, whenever the pressure within the cylinder 11 exceeds thepreselected value to cause the domed portion 47 to move to the concaveposition, the surface 52 of the flexible member 51 tightly engages thedished, partially frosted surface 48 of the translucent window 22. Theindentations 53 form an air space permitting light to be reflected fromthe differently colored indentations, and thus, the indentations areclearly visible through the frosted areas of the translucent window 22,as illustrated in FIG. 4. As described hereinabove, tight engagementbetween the surface 52 of the flexible member 51 and the partiallyfrosted dished surface 48 of the translucent window 22 renders the clearareas 49 visibly indistinct, and therefore, only the indentationsforming the word "FULL are visible.

The housing 24 may have a configuration permitting threaded engagementwith a threaded aperture formed within the cylinder or within a fittingattached to the cylinder in a manner to provide fluid communicationbetween an interior of the cylinder and a side surface of theoil-canning disc opposite of the translucent window.

Although various modifications might be suggested by those versed in theart, it should be understood that I wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably andproperly come within the scope of my contribution to the art.

I claim as my invention:

1. A device for indicating pressure above or below a preselected valuecomprising:

means forming a housing;

means forming a disc disposed within said housing means and having acentrally disposed, domed portion movable from a normal convex positionto a concave position in response to an increase of pressure above thepreselected value applied inwardly of the domed portion in the normalconvex position;

means forming a translucent window overlying said disc means and havinga surface disposed juxtapositionally to said disc means partiallyfrosted to form both clear and frosted areas and having a dishedconfiguration formed complementary to said domed position of said discmeans; and

means transmitting pressure to said domed portion of said disc meanswhereby said domed portion moves into tight engagement with said surfacein response to an increase in the transmitted pressure above thepreselected value to obliterate visual distinctions between said clearareas and said frosted areas, and said domed portion moves out ofengagement with said surface in response to a decrease in pressure belowthe preselected value to render said clear areas visible to indicate apressure below the preselected value.

2. A device for indicating pressure as defined in claim 1 and furthercomprising:

means forming a flexible member coextensive with said disc means andadhered to a surface of said disc juxtaposed to said dished surface ofsaid translucent window means and movable with said domed portion intoand out of engagement with said surface of said translucent window;

said flexible member having indentations formed in a surface thereofjuxtaposed to said dished surface, whereby said indentations becomevisible whenever an increase in the transmitted pressure above thepreselected value moves said domed portion to the concave positioncausing said flexible member to tightly engage said dished surface toindicate a pressure above the preselected value.

3. A device for indicating pressure as defined in claim 1 and furthercharacterized by:

said housing means having a bore therethrough formed with an enlargedportion and a reduced diameter portion forming an interior, annularshoulder portion;

said disc means having a circular configuration sized to fit within saidenlarged portion of said bore and including a peripheral, annularportion seated against said shoulder; said translucent window meanshaving a circular configuration sized to fit within said enlargedportion of said bore and including an annular peripheral portion engagedagainst said annular portion of said disc means on a side thereofopposite said shoulder; and

means having an annular configuration and tightly engaged within saidenlarged portion of said housing bore for retaining said translucentwindow means and said disk means within said housing.

4. In a fire extinguisher including a cylinder containing pressurizedfire extinguishing material, a device for indicating the amount ofpressurized fire extinguishing material contained within the cylindercomprising:

means forming a housing;

means forming a disc disposed within said housing means and having acentrally disposed, domed portion movable from a normal convex positionto a concave position in response to an increase of pressure above thepreselected value applied inwardly of the domed portion in the normalconvex position;

means forming a translucent window overlying said disc means and havinga surface disposed juxtapositionally to said disc means partiallyfrosted to form both clear and frosted areas and having a dishedconfiguration formed complementary to said domed portion of said discmeans; and means providing fluid communication between an interior ofthe fire extinguisher and a side of said disc opposite of said windowmeans to transmit pressure to said domed portion of said disc means,whereby said dorned portion moves into tight engagement with saidsurface in response to an increase in the transmitted pressure above thepreselected value to obliterate visual distinctions between said clearareas and said frosted areas, and said domed portion moves out ofengagement with said surface in response to a decrease in pressure belowthe preselected value to render said clear areas visible to indicate aninsufficient amount of fire extinguishing material contained within thecylinder to render the extinguisher operable.

5. In a fire extinguisher, a device as defined in claim 4 and furthercharacterized by:

means forming a flexible member coextensive with said disc means andadhered to a surface of said disc juxtaposed to said dished surface ofsaid translucent window means and movable with said domed portion intoand out of engagement with said surface of said translucent window; saidflexible member having indentations formed in a surface thereofjuxtaposed to said dished surface, whereby, said indentations becomevisible whenever an increase in pressure above the preselected valuemoves said domed portion to the concave position causing said flexiblemember to tightly engage said dished surface to indicate a sufficientamount of fire extinguishing material contained within the cylinder torender the extinguisher operable.

6. In a fire extinguisher, a device as defined in claim 4 and furthercharacterized by:

said housing means having a bore therethrough formed with an enlargedportion and a reduced diameter portion forming an interior, annularshoulder portion; said disc means having a circular configuration sizedto fit within said enlarged portion of said bore and including aperipheral, annular portion seated against said shoulder; saidtranslucent window means having a circular configuration sized to fitwithin said enlarged portion of said bore and including an annularperipheral portion engaged against said annular portion of said discmeans on a side thereof opposite said shoulder; and means having anannular configuration and tightly engaged within said enlarged portionof said housing bore for retaining said translucent window means andsaid disc means within said housing. 7. In a fire extinguisher, a deviceas defined in claim 4 and 5 5 further characterized by:

the cylinder containingv the pressurized fire extinguishing materialhaving an aperture formed in a side wall thereof; and said housing meanshaving a cylindrical portion sealingly engaged within said aperture in amanner to provide fluid communication between an interior of thecylinder and a surface of said disc opposite said translucent window. 8.In a fire extinguisher, a device as defined in claim 4 and furthercharacterized by:

said clear areas formed on said dished surface of said translucentwindow means configured in the form of the word "EMPTY when viewed froma side of the window opposite said dished surface. 9. In a fireextinguisher, a device as defined in claim 5 and 70 furthercharacterized by:

said indentations formed in said flexible member configured to spell theword FULL when viewed through said translucent window. 10. A device forindicating when the pressure in a recepta- 75 cle is above or below apredetermined value comprising a housing means, a diaphragm means havingfirst and second side surfaces, said first side surface adapted to be inpressure communication with said receptacle, said diaphragm means beingmovable between a first position and a second position in response tochanges in pressure on said first side surface above and below saidpredetermined value, a translucent viewing means having an inner surfaceat least a portion of which is adjacent said second surface of saiddiaphragm means, said inner surface of said viewing means beingrelatively frosted except for at least one portion which is relativelyclear whereby when said pressure is above said predetermined value saidsecond surface of said diaphragm means will be in said second positionin contact with said inner surface of said viewing means to obscure thedifi'erences between said relatively frosted and relatively clearportions and whereby when said pressure is below said predeterminedvalue said diaphragm means will be in said first position with saidsecond surface out of contact with said inner surface of said viewingmeans so that said relatively clear area will be readily distinguishablefrom said relatively frosted area.

11. A device according to claim 10 wherein said diaphragm means hasindicia on said second surface thereon whereby when said diaphragm meansis in said second position said indicia will be clearly visible throughsaid viewing means but when said diaphragm is in said first positionsaid indicia will be obscured so as not to be readily visible throughsaid relatively frosted portion.

12. A device according to claim 11 means is formed by indentations insaid diaphragm means.

13. A device according to claim 12 wherein said indentations have abright color therein to enhance their visibility in said secondposition.

wherein said indicia second surface of said 14. A device according toclaim 12 wherein said diaphragm means includes first and each other.

15. A device according to claim 1 wherein said clear portions of saidviewing means are formed by indentations in the inner surface of saidviewing means.

i t I II I second members tightly adhered to

1. A device for indicating pressure above or below a preselected valuecomprising: means forming a housing; means forming a disc disposedwithin said housing means and having a centrally disposed, domed portionmovable from a normal convex position to a concave position in responseto an increase of pressure above the preselected value applied inwardlyof the domed portion in the normal convex position; means forming atranslucent window overlying said disc means and having a surfacedisposed juxtapositionally to said disc means partially frosted to formboth clear and frosted areas and having a dished configuration formedcomplementary to said domed portion of said disc means; and meanstransmitting pressure to said domed portion of said disc means wherebysaiD domed portion moves into tight engagement with said surface inresponse to an increase in the transmitted pressure above thepreselected value to obliterate visual distinctions between said clearareas and said frosted areas, and said domed portion moves out ofengagement with said surface in response to a decrease in pressure belowthe preselected value to render said clear areas visible to indicate apressure below the preselected value.
 2. A device for indicatingpressure as defined in claim 1 and further comprising: means forming aflexible member coextensive with said disc means and adhered to asurface of said disc juxtaposed to said dished surface of saidtranslucent window means and movable with said domed portion into andout of engagement with said surface of said translucent window; saidflexible member having indentations formed in a surface thereofjuxtaposed to said dished surface, whereby said indentations becomevisible whenever an increase in the transmitted pressure above thepreselected value moves said domed portion to the concave positioncausing said flexible member to tightly engage said dished surface toindicate a pressure above the preselected value.
 3. A device forindicating pressure as defined in claim 1 and further characterized by:said housing means having a bore therethrough formed with an enlargedportion and a reduced diameter portion forming an interior, annularshoulder portion; said disc means having a circular configuration sizedto fit within said enlarged portion of said bore and including aperipheral, annular portion seated against said shoulder; saidtranslucent window means having a circular configuration sized to fitwithin said enlarged portion of said bore and including an annularperipheral portion engaged against said annular portion of said discmeans on a side thereof opposite said shoulder; and means having anannular configuration and tightly engaged within said enlarged portionof said housing bore for retaining said translucent window means andsaid disk means within said housing.
 4. In a fire extinguisher includinga cylinder containing pressurized fire extinguishing material, a devicefor indicating the amount of pressurized fire extinguishing materialcontained within the cylinder comprising: means forming a housing; meansforming a disc disposed within said housing means and having a centrallydisposed, domed portion movable from a normal convex position to aconcave position in response to an increase of pressure above thepreselected value applied inwardly of the domed portion in the normalconvex position; means forming a translucent window overlying said discmeans and having a surface disposed juxtapositionally to said disc meanspartially frosted to form both clear and frosted areas and having adished configuration formed complementary to said domed portion of saiddisc means; and means providing fluid communication between an interiorof the fire extinguisher and a side of said disc opposite of said windowmeans to transmit pressure to said domed portion of said disc means,whereby said domed portion moves into tight engagement with said surfacein response to an increase in the transmitted pressure above thepreselected value to obliterate visual distinctions between said clearareas and said frosted areas, and said domed portion moves out ofengagement with said surface in response to a decrease in pressure belowthe preselected value to render said clear areas visible to indicate aninsufficient amount of fire extinguishing material contained within thecylinder to render the extinguisher operable.
 5. In a fire extinguisher,a device as defined in claim 4 and further characterized by: meansforming a flexible member coextensive with said disc means and adheredto a surface of said disc juxtaposed to said dished surface of saidtranslucent window means and movable with said domed portion into andout of engagement with said surface of Said translucent window; saidflexible member having indentations formed in a surface thereofjuxtaposed to said dished surface, whereby, said indentations becomevisible whenever an increase in pressure above the preselected valuemoves said domed portion to the concave position causing said flexiblemember to tightly engage said dished surface to indicate a sufficientamount of fire extinguishing material contained within the cylinder torender the extinguisher operable.
 6. In a fire extinguisher, a device asdefined in claim 4 and further characterized by: said housing meanshaving a bore therethrough formed with an enlarged portion and a reduceddiameter portion forming an interior, annular shoulder portion; saiddisc means having a circular configuration sized to fit within saidenlarged portion of said bore and including a peripheral, annularportion seated against said shoulder; said translucent window meanshaving a circular configuration sized to fit within said enlargedportion of said bore and including an annular peripheral portion engagedagainst said annular portion of said disc means on a side thereofopposite said shoulder; and means having an annular configuration andtightly engaged within said enlarged portion of said housing bore forretaining said translucent window means and said disc means within saidhousing.
 7. In a fire extinguisher, a device as defined in claim 4 andfurther characterized by: the cylinder containing the pressurized fireextinguishing material having an aperture formed in a side wall thereof;and said housing means having a cylindrical portion sealingly engagedwithin said aperture in a manner to provide fluid communication betweenan interior of the cylinder and a surface of said disc opposite saidtranslucent window.
 8. In a fire extinguisher, a device as defined inclaim 4 and further characterized by: said clear areas formed on saiddished surface of said translucent window means configured in the formof the word ''''EMPTY'''' when viewed from a side of the window oppositesaid dished surface.
 9. In a fire extinguisher, a device as defined inclaim 5 and further characterized by: said indentations formed in saidflexible member configured to spell the word ''''FULL'''' when viewedthrough said translucent window.
 10. A device for indicating when thepressure in a receptacle is above or below a predetermined valuecomprising a housing means, a diaphragm means having first and secondside surfaces, said first side surface adapted to be in pressurecommunication with said receptacle, said diaphragm means being movablebetween a first position and a second position in response to changes inpressure on said first side surface above and below said predeterminedvalue, a translucent viewing means having an inner surface at least aportion of which is adjacent said second surface of said diaphragmmeans, said inner surface of said viewing means being relatively frostedexcept for at least one portion which is relatively clear whereby whensaid pressure is above said predetermined value said second surface ofsaid diaphragm means will be in said second position in contact withsaid inner surface of said viewing means to obscure the differencesbetween said relatively frosted and relatively clear portions andwhereby when said pressure is below said predetermined value saiddiaphragm means will be in said first position with said second surfaceout of contact with said inner surface of said viewing means so thatsaid relatively clear area will be readily distinguishable from saidrelatively frosted area.
 11. A device according to claim 10 wherein saiddiaphragm means has indicia on said second surface thereon whereby whensaid diaphragm means is in said second position said indicia will beclearly visible through said viewing means but when said diaphragm is insaid first position said indicia will be obscured so as not to bereadily visible through said relativEly frosted portion.
 12. A deviceaccording to claim 11 wherein said indicia means is formed byindentations in said second surface of said diaphragm means.
 13. Adevice according to claim 12 wherein said indentations have a brightcolor therein to enhance their visibility in said second position.
 14. Adevice according to claim 12 wherein said diaphragm means includes firstand second members tightly adhered to each other.
 15. A device accordingto claim 1 wherein said clear portions of said viewing means are formedby indentations in the inner surface of said viewing means.